Method for burning clay slate or clay



Aug. 9, 1960 H. A. AR. HoLMy METHOD 'OR BURNING CLAY SLATE O R CLAYFiled Nov. 5, 1956 arent Patented Aug. 9, 19%() tice METHOD FOR BURNlNGCLAY SLATE OR CLAY arry Alfred Reinhold Holm, Claesborg, Skovde, SwedenFiled Nov. 5, 1956, Ser. No. 620,510

Claims priority, application Sweden Nov. 4, 1955 1 Claim. (Cl. 10G-40)The present invention refers to a method and an oven for the burning Yofclay slate, clay and similar materials. The invention is primarilyintended to be made use of for the production of such porous clinkerwhich is used as a filling material in the manufacture of lightconcrete, but it may also be employed for other purposes, for instancefor the production of basic materials for the manufacture of porousconcrete. In the production of porous clinker, raw material in the formof clay slate or clay of that kind is made use of, which is able whenheated to develop gas at sintering, the material, crushed into pieces orgrains of a suitable size, being then spread out over the bottom hearthof the oven, where it is subjected to the inuence of hot gases. It isknown for this purpose to employ an oven With'a rotating bottomhearth,on which the material is spread out in a thin layer, which is caused bythe rotation of the bottom hearth to pass through a heating zone,wherein the material is subjected to so high a temperature that anenamel layer is formed on the surface of the grains and the grains areenlarged by the development of gas. This method and this oven type havethe disadvantage that the granular material tends, by reason of thesintering, to stick to the bottom hearth, the ma-.

terial thus adhering to the hearth being lost for the production. Themethod also has the drawback that the adhering material will by degreesform a cake of sintered material on the bottom hearth, such cake havingto be removed from time to time. Furthermore, diiculties are met with ineffecting a uniform spreading of the material grains on the rotatingbottom hearth, which results in that the grains will partly sintertogether into larger pieces that will then have to be crushed.

The present invention has for its object to prevent the material fromsticking to the bottom hearth. To this end the material is subjectedduring its passage through the heating zone to cooling from below tosuch an extent that adhering `sintering to the bottom hearth isprevented, Whereas the material is otherwise heated in the requisitedegree to permit gas development to take place at a simultaneousformation of an enamel layer on the surface of the grains. According tothe invention this treatment with cooling from below simultaneousheating by means of hot gases from above takes place, while the materialperforms a progressive movement over the bottom hearth, which iseffected by vibrating or oscillating the bottom hearth in the horizontalplane or in a plane sloping toward the' outlet. The reciprocatingmovement of the bottom hearth has the advantage that the incomingmaterial is distributed uniformly over the surface of the bottom hearth,so that the material forms a single layer of grains separated from oneanother. The cooling is effected by cooling of the bottom hearth,preferably by means of air or gases which are pressed through the bottomhearth, which latter preferably consists of a material pervious to air,such as chamotte. Burning of the material may in this way take place incontinuous operation at a conly progressive movement of the materialover the am hearth.

As a raw material for the production of porous clinker, dried clay orclay slate is preferably made use of, said material having been crushedto pieces or grains of suitable sizes of 8-20 millimeters, for example.In the crushing operation, a certain quantity of finely crushed materialbelow said size is obtained, which material would hitherto be conceivedof as constituting a loss of material e amounting as far as up to about30%. According to the present invention, said finely crushed materialmay be utilized by grinding, silting and forming the material intogranules, which are dried so `as to yattain the requisite strength. Thematerial consisting of granules may be used either alone or preferablytogether with crushed material of a larger grain size as a basicmaterial for the production of porous clinker. At the production ofmaterial in the form of granules, a material such as iron may be added,which is adapted to bring about an increased formation of pores duringthe heating operation. Furthermore, a cement may be added to impart tothe granules the requisite strength for transport.

In the manufacture of porous concrete, oil-bearing clay slate in theform of pieces or grains is preferably used as raw material, such piecesof grains having dimensions of 2li-3 millimeters, the clay slate beingthen preferably mixed with crushed limestone. A mixture of materials ofthis kind may be advantageously burned according to the presentinvention. In this case the raw material may also be worked intogranules consisting of amixture of ground clay slate andlimestonepowder. Obviously, the material may also be constituted by a mixture ofcrushed clay slate and granules. The reciprocating movement of thebottom hearth has the advantage that the burning may take place incontinuous operation.

The invention will be described more closely with reference to theaccompanying drawing, which illustrates an oven construction accordingto the invention. Fig. 1 is a vertical section through they, oven andFig. 2 ya section on line 2-2 in Fig. 1.

Combined with the burning oven is'a preheater inthe form of a verticaloven 1, which is placed on the main oven and which communicates at thebottom with a channel 2 serving at the same time as an inlet for thematerial 3 coming from the preheater and as an outlet for the hotcombustion gases. 'Ihe material in the form of pieces or grains to beburned is introduced into the upper part of the preheater through afilling funnel 4, and is advanced downwardlythrough the preheater bymeans of a suitable `contrivance which is in the drawing only indicatedby a chain-dotted line 5 and which may consist of a worm, for example,which is driven from a' shaft 6 through a bevel gearing 7. 'Ihe gasesescaping from the oven are sucked out by means of a fan -8 arranged atthe top on the preheater, the gases then serving to preheat the materialto a suitable 'temperature such as approximately 500 C. The channel Zcontinues downwardly through the heating zone 9 to a channel 10, throughwhich the completely treated material escapes to a conveyer or the like,not shown. The heating is effected by means of a number of oil-burners12 arranged in the oven roof 11, said burners being supplied withprimary air for the combustion.

The bottom hearth located between the inlet 2 and the outlet 10 is of aheight diminishing in a stepwise fashion toward the outlet, and consistsof lire bricks forming a number of stair blocks 13, preferably withupper sides sloping slightly toward the outlet. The blocks are carriedby perforated plates 14 covering the lower sides of the blocks. Theblocks 13 are built groupwise into the chamber 15, which is suppliedwith secondary air through pipes 15 for the cooling of the bottomhearth. The whole of the bottom hearth with its associated equalizingchambers is built into a framework 17, which in the example Shown isformed into a saddle adapted to slide back and forth on a substructure18 sloping downwardly toward the outlet. The framework may instead beadapted to run on wheels or roller bearings. The frame is connected to amotor 19 through the intermediary of a gearing 20 and a transmissiondevice 21 shown diagrammatically in the drawing, through which therotary movement is transformed into a reciprocating movement of theframe 17, whereby a vibrating or oscillatory movement is imparted to thebottom hearth in a plane sloping toward the outlet. However, the frame17 and the bottom hearth may also be movable in a horizontal plane. Theheating zone 9 is delimited inwardly by brick wall 22, below which theinner portion of the bottom hearth is movable in the closestpossibleproximity to the wall. As will be seen from Fig. 2, the ovenchamber is delimited outwardly by means of water seals 23.

The raw material pretreated and dried in the manner above described isintroduced into the preheater 1, where it meets warmer and warmer gases,and from which it is slowly vdischarged into the channel 2 at atemperature of approximately 500 C., the material then sliding along thesloping upper side of the wall 22 and falling down onto the bottomhearth beside said wall. Through the oscillatory movement of the bottomhearth the material is spread uniformly over the surface of the hearth,while a progressive movement is at the same time imparted to thematerial over the hearth in the direction of movement of the lattertoward the outlet 10. The individual grains of the material then performa sliding movement over the various steps 13 as well as a rollingmovement when passing from one step to the next following step. Throughthe secondary air supplied from below and pressed through the porousblocks 13, the grains of the material moving on the hearth are cooledfrom below while being simultaneously heated successively to thesintering temperature (about 1200 C.) during the passage through thezone 9, the grains then expanding by reason of thel gas development, andan enamel layer forming on the surfaceof the grains. When the completelytreated material falls down into the outlet 10, it

is cooled very rapidly, so that the surface of the grains will not haveltime to crystallize but becomes amorphous, whereby the material will beable readily to form chemical compounds with the material, into whichthe clinker material is mixed.

Ihe rate of movement of the material over the bottom hearth may beadapted to the nature of the material by varying the length of strokeand the number of strokes per minute of the bottom hearth at a controlof the temperature by means of the burners and the cooling air. Toprovide for a longer burning time, a plurality of ovens may be coupledin series, so that the same material will be heated successively in thevarious ovens under thev same or varying temperature conditions, theovens being then preferably located at different levels above oneanother, so that the material may be fed directly from one oven into thenext following oven. The total burning time per oven may then amount toapproximately 8 utes.

What is claimed is:

A method of producing porous clinker from granules of a materialselected from the group consisting of clay and clay slate, comprisingdischarging the material into a gas-filled heating chamber of an oven,depositing the material onto a bottom hearth of the oven so as to form asingle layer of the granules thereon, vibrating the bottom hearth so asto cause the granules to be spread apart and to advance in directcontact with an upper surface of the hearth, the granules beingseparated from one another only by the gases of the heating chamber,heating the layer of granules from above so as to cause expansion andsintering of the granules, and cooling the bottom hearth so Vas toprevent the sintered granules from sticking to the hearth, therebyallowing the granules to move freely along the surface of the hearth andapart from one another.

References Cited in the iile of this patent UNITED STATES PATENTS346,358 Dickson July 27, 1886 849,873 Wentz Apr. 9, 41907 939,936 WieyNov. 9, 1909 1,021,509 Dwight Mar. 26, 1912 1,747,740 Smith Feb. 18,1930 1,982,918 Marty Dec. 4, 1934 2,029,524 Denning Feb. 4, 19362,163,513 Douglas June 20, 1939 2,230,831 Douglas Feb. 4, 1941t2,521,591 Martin Sept. 5, 1950 2,650,171 Schaaf Aug. 25, 1953 2,721,805Burke Oct. 25, 1955 2,782,019 Turney et al. Feb. 19, 1957 2,786,772Steward et al Mar. 26, 1957 FOREIGN PATENTS 421,973 Great Britain Dec.24, 1934 min-

